Chemical mechanical planarization (CMP) is a process well-known in the art for processing surfaces of a semiconductor wafer. Planarization, in effect, polishes away a portion of the wafer's surface to form an ultra-smooth exposure upon which additional processing layers may be formed. CMP utilizes both a “mechanical” polishing pad to convey pressure which, in combination with tightly-controlled particulate material (component of polishing slurry) abrasively remove some material, as well as at least one chemically-reactive agent (component of polishing slurry) to initiate an “etching” or softening of surface materials. Over time, the polishing pad is known to experience buildup of excess compacted polishing slurry solids, hardened urethane pad materials (in response to heat, mechanical work, process chemicals, etc.), reacted materials and wafer debris, globally referred to as “glazing”. In the art, therefore, it has become desirable to continually clean (“condition” or “dress”) the polishing pad by removing trapped slurry and unmatting (re-expanding and/or texturing with mechanically ‘cut’ furrows) the pad material.
A number of conditioning procedures and apparatus have been developed. One conventional conditioner comprises an arm for holding a conditioner head with an abrasive disk facing the polishing pad. A bearing system rotatably supports the abrasive disk at the end of the arm. The abrasive disk rotates against the polishing pad to physically abrade the polishing pad and remove the glazing layer from the pad's surface.
While the abrasive disk is rotating against the polishing pad, slurry will tend to coat the edges and surfaces of the abrasive conditioning disk, as well as splash on the conditioner head itself. When the conditioner head is not operating (for example, between polishing operations), the slurry remaining on the abrasive disk and conditioner head can build up to form a hardened, caked surface. During the next polishing operation, therefore, the residual slurry film and particles may dislodge and fall onto the polishing pad and scratch the surface of the wafer being processed. The build-up or “fouling” commonly forms between abrasive grains, which service to decrease the abrasive particle exposure, which over time can reduce the abrasive penetration and thereby effectiveness of the conditioner. In systems where the chemistry may be modified between polishing and/or conditioning cycles, chemically dislodged material may further result in cross-contaminating subsequent wafers being processed.
The prior art has proposed various types of “cleaning cups” in which the conditioner head may be positioned when not being used, where the cups can be likened to a bath for the head, maintaining any slurry in a sufficiently liquid state to avoid the formation of hardened slurry particles during subsequent conditioning processes.
Initial prior art “cleaning cups” consisted of a bath of deionized water (or another cleaning fluid), which would hold the conditioner head in a submerged position between conditioning operations. U.S. Pat. No. 6,217,430 issued to R. Koga et al. on Apr. 17, 2001 discloses a prior art cleaning cup improvement over this basic arrangement, using a spray nozzle for spraying a cleaning solution on the top side of the conditioner head while the underside of the head (supporting the abrasive disk) remain submerged in the cleaning cup bath. U.S. Pat. No. 6,481,446 issued to M-S Yang et al. on Nov. 19, 2002 discloses an alternative cleaning cup structure, in this case including an apertured bottom support for allowing an injected inert gas to bubble up through the cleaning bath and assist in the removal of particles that are sticking to the abrasive conditioning disk. In a further example, U.S. Pat. No. 7,025,663 issued to T-B Kim on Apr. 11, 2006 describes a cleaning cup including a similar bubbler structure as taught by Yang et al., used in combination with a U-shaped spraying pipe that is provided with a plurality of nozzles to spray downward onto the conditioner head.
While these various prior art arrangements are considered improvements over the conventional “static bath”, they have not been successful in completely removing all of the particulate residue from the conditioning head. It has been found that some of the slurry debris will remain adhered to the conditioner head, including the abrasive surface, resulting in a condition now referred to as “disk fouling”—the remaining residue causing a mechanical change in the abrasive quality of the conditioner head surface.
Thus, a need remains in the art for an arrangement that will successfully remove most, if not all, of the adherent residue from a CMP system conditioner head.